Correlating metastable-atom density, reduced electric field, and electron energy distribution in the post-transient stage of a 1-Torr argon discharge

Abstract

Temporal measurement of electron density, metastable-atom density, and reduced electric field are used to infer the dynamic behavior of the excitation rates describing electron-atom collision-induced excitation in the positive column of a 1 Torr argon plasma by invoking plausible assumptions regarding the shape of the electron energy distribution function performed in Adams et al (2012 Phys. Plasmas 19 023510). These inferred rates are used to predict the 420.1 nm to 419.8 nm argon emission ratio, which agree with experimental results when the assumptions are applicable. Thus the observed emission ratio is demonstrated to be dependent on the metastable-atom density, electron density, and reduced electric field. The established confidence in the validity of this emission-line-ratio model allows us to predict metastable argon-atom density during the post-transient phase of the pulse as suggested by De Joseph et al (2005 Phys. Rev. E 72 036410). Similar inferences of electron density and reduced electric field based on readily available diagnostic signatures may also be afforded by this model. Keywords: optical emission spectroscopy (OES), 420.1-419.8 nm emission-line ratio, 1s 5 metastable argon atom, reduced electric field (E/N), electron energy distribution, time-resolved, extended corona model

Comment on ‘Correlating metastable-atom density, reduced electric field, and electron energy distribution in the post-transient stage of a 1 Torr argon discharge’ (2015Plasma Source Sci. Technol.24034009)

“…Considering the above remarks, one can conclude that the electron densities reported by Franek et al [1] are not correct and consequently the conclusion they have driven regarding the validity of the method for the estimate of argon metastable density from the 420.1/419.8 nm emission intensity ratio is not justified.…”

“…The resonance cavity technique is based on a perturbation treatment of the electron-microwave interaction [3,7] assuming that the cavity mode is only weakly perturbed and the E-field distribution inside the cavity remains almost unchanged. So the measured frequency shifts by Franek et al [1] cannot provide the correct electron densities present inside the μ-wave cavity.…”

“…In their publication, Franek et al [1] do not give neither the μ-wave frequency nor the resonance cavity dimensions and they only indicate that this later works on mode TM 010 . But referring to the recent paper of Barnat and Weatherford [4] one can guess that Franek et al [1] have used the same cylindrical resonance cavity than in 4, with its resonance frequency at 2.2 GHz. For the TM modes of a cylindrical cavity, resonance frequencies f are linked to the radius R c and length L of the cavity by the relation [5]:…”

“…For the r p = 1.27 cm radius of the plasma tube used by Franek et al [1], the overlapping factor calculated by numerical integration is:…”

“…Experimental results of Franek et al [1] are analyzed in terms of density ratios n e /n 0 , where n 0 = 3.2 × 10 16 cm −3 is the argon atom density at their working pressure of 1 Torr and room temperature. Data points shown in figures 5-7 of their paper [1] …”